An iterative difference-dedicated configuration interaction. Proposal and test studies

An earlier work proposed a difference-dedicated configuration interaction method based on effective Hamiltonian arguments and was essentially devoted to the calculation of transition energies and binding energies. Using the resulting density matrices, the procedure may be made independent of the choice of starting molecular orbitals. This iterative redefinition of the MOs improves the quality of the results, as shown by comparing to full-CI results on CH2, CH2+ and SiH2 vertical and adiabatic transition energies. The efficiency of the method for the treatment of weakly avoided crossings and for the determination of binding energies is illustrated on the LiF molecule. The mean deviation of the iterative difference-dedicated CI results to FCI energy differences is lower than 0.1 eV.